The use of various thermoplastic resins to make fibers and fabrics is well known. In particular, propylene-based polymers and copolymers (sometimes referred to as propylene-based elastomers) are well known in the art for their usefulness in a variety of applications, including the manufacture of nonwoven fabrics. Such fabrics have a wide variety of uses, such as in medical and hygiene products, clothing, filter media, and sorbent products. Nonwoven fabrics are particularly useful in hygiene products, such as baby diapers, adult incontinence products, and feminine hygiene products. An important aspect of these fabrics, particularly in hygiene applications, is the ability to produce aesthetically pleasing fabrics having good leakage performance at low cost.
Propylene impact copolymers are a another type of thermoplastic resin, commonly used in applications where strength and impact resistance is desired such as in molded and extruded automobile parts, household appliances, luggage and furniture. Propylene homopolymers are often unsuitable for such applications because they are too brittle and have low impact resistance particularly at low temperature, whereas propylene impact copolymers are specifically engineered for applications such as these.
Though often used to make films, propylene impact copolymers are not as commonly used to make fibers and fabrics because impact resistance is often not a desired property for such applications. For fibers and fabrics, manufacturers focus on properties such as strength, processability, softness and breathability. U.S. Pat. Nos. 6,440,882 and 6,248,833 and U.S. Patent Application Nos. 2009/0311938 and 2009/0149605 describe fibers and fabrics prepared with impact copolymers.
In many hygiene applications, multilayer nonwoven materials or laminates are employed having at least one elastic core layer and at least one extensible facing layer, where the elastic layer provides the desired conformability and fit of the product (and therefore good leakage performance) while the extensible facing layer provides the desired aesthetics. While propylene-based elastomers are commonly used to form such elastic layers, the facing layers are often composed of bicomponent polymer blends. Such blends may include homopolymers of propylene, homopolymers of ethylene, random propylene copolymers, and other propylene or ethylene-based polymers and blends thereof, where the blends have a core/sheath structure. The formation of such bicomponent materials, however, adds complexity to nonwoven manufacturing processes. It would be desirable, then, as one embodiment of the present invention, to provide monocomponent nonwoven fibers and fabrics having good extensibility and good spinnability in spunmelt processes.
We have found that nonwoven fibers and fabrics prepared from blends of propylene impact copolymers and propylene-based elastomers provide high cross-direction elongation and good spinnability in nonwoven manufacturing processes, especially those equipped with monocomponent spinnerets.